Transcripts of intercepted calls between Flynn and Russian ambassador to the US, Sergey Kislyev, as described by US officials to various news outlets, showed the two had discussed sanctions ahead of Trump’s inauguration, when Flynn was part of the transition team but not in post as national security adviser.

Sanctions had been imposed by then-President Barack Obama after US agencies concluded Moscow had interfered in the US election campaign.

In his resignation letter, Flynn conceded that he had misled the vice-president Mike Pence, who had previously publicly denied that Flynn had discussed sanctions with Kislyev. Flynn wrote:

Unfortunately, because of the fast pace of events, I inadvertently briefed the vice-president-elect and others with incomplete information regarding my phone calls with the Russian ambassador.

I have sincerely apologized to the president and the vice president, and they have accepted my apology.

Keith Kellogg has been appointed acting national security adviser. He – along with David Petraeus, who meets Trump at the White House on Tuesday, and Robert Harward – are in the running to succeed Flynn.

But Trump during the campaign spoke sympathetically about Petraeus, despite his frequent criticisms of his Democratic opponent Hillary Clinton for mishandling classified materials. Petraeus was briefly under consideration to become secretary of state before Trump picked Exxon CEO Rex Tillerson.

David Petraeus. Photograph: Jason Reed/Reuters

Robert Harward

Robert Harward, a Navy Seal and retired vice-admiral, served as deputy commander of the United States central command when it was under the command of General James Mattis, who is now secretary of defense.

He served on the National Security Council for President George W Bush and commissioned the National Counter Terrorism Center.

Upon retirement in 2013 after a nearly 40-year career in the Navy, Harward took a post as a chief executive officer for defense and aerospace giant Lockheed Martin in the United Arab Emirates. Trump has recently been in very public negotiations with Lockheed over the cost of its F-35 fighter jet program.

Who is Keith Kellogg?

Alan Yuhas

Kellogg, 72, named as Trump’s acting national security adviser, was born in Ohio and served 36 years in the military: in the army in Vietnam, as a special forces officer in Cambodia, and during the first Iraq war as chief of staff for the 82nd Airborne Division.

He rose to command the airborne division from 1997 to 1998 and later came to national prominence when he served as chief operating officer for Baghdad’s provisional government through 2004 – a year of mistakes by the transitional administration that haunted Iraq through the next decade of war.

After his retirement Kellogg joined a series of contracting firms including tech giant Oracle and defense contractor Cubic Defense.

The retired general has kept a low profile in the White House compared with his predecessor. He was granted a formal role in Trump’s transition team and later named chief of staff and executive secretary of the National Security Council, making him one military counterweight to an unusually prominent civilian on the council, Trump’s chief strategist, Steve Bannon.

Summary

Julian Borger

The US national security adviser, Michael Flynn, resigned late on Monday night amid a flow of intelligence leaks that he had secretly discussed sanctions with the Russian ambassador to Washington and then tried to cover up the conversations.

The resignation, with the Trump era less than four weeks old, is the latest and most dramatic convulsion in the most chaotic start to an administration in modern US history.

It was far from clear whether Flynn’s departure would steady an inexperienced and feuding White House, or resolve the lingering suspicions about the Trump team’s pre-election contacts with the Kremlin.

The White House issued a statement just after 11pm in Washington announcing the resignation, shortly after reports broke that the Trump administration had been warned weeks ago that Flynn might be vulnerable to Russian blackmail.

The statement also named retired army general Joseph Keith Kellogg as acting national security adviser, pending the appointment of a permanent successor. It was reported that a third general, former CIA director David Petraeus, was due to meet Trump on Tuesday.

In his resignation letter, Flynn claimed he had mistakenly misled vice-president Mike Pence and other Trump officials about the nature of phone calls in December to the Russian ambassador, Sergei Kisilyak. When intelligence leaks about the communications began appearing last month, Pence and other White House officials insisted the contact had involved only an exchange of Christmas greetings and arrangements for a future phone conversation between Trump and Vladimir Putin.

However, subsequent leaks suggested that they had been more substantial, and concerned sanctions the Obama administration was about to impose on Moscow for interference in the presidential elections. Intelligence officials claimed that Flynn had given the impression the sanctions might be lifted once the Trump administration came to office on 20 January.

Trump security adviser Flynn quits after claims he secretly spoke with Russia, then lied about it

Republican Devin Nunes, chair of the House intelligence committee, is the first supportive voice I’ve so far seen for Flynn since news broke of his resignation:

Michael Flynn served in the US military for more than three decades. Washington DC can be a rough town for honorable people, and Flynn – who has always been a soldier, not a politician – deserves America’s gratitude and respect for dedicating so much of his life to strengthening our national security.

Flynn’s resignation letter doesn’t go into detail of his communications with the Russian ambassador to the US, Sergey Kislyev.

Transcripts of intercepted calls, though, as described by US officials to various news outlets, showed that the two had discussed sanctions – although not necessarily going so far as Flynn promising that Trump would lift them.

The conversations have been described as “potentially illegal” because of the 1799 Logan Act, which bans private citizens from negotiating with countries with which the US is in dispute. The calls were made before Trump’s inauguration, when Flynn was part of the transition team but not in post as national security adviser.

But many have said the wider issue is the extent of any collusion between Russia and the Trump administration. That issue remains unresolved by Flynn’s ousting.

As with the travel ban, Sally Yates – the former acting attorney general, fired from that role by Trump after she advised justice department lawyers that the executive order was “not lawful” – finds herself at the centre of this story.

As the Washington Post reports, Yates reported to the White House in January her concerns over Flynn’s potential susceptibility to blackmail due to his communications with Russia:

The acting attorney general informed the Trump White House late last month that she believed Michael Flynn had misled senior administration officials about the nature of his communications with the Russian ambassador to the United States, and warned that the national security adviser was potentially vulnerable to Russian blackmail, current and former U.S. officials said.

The message, delivered by Sally Q. Yates and a senior career national security official to the White House counsel, was prompted by concerns that ­Flynn, when asked about his calls and texts with the Russian diplomat, had told Vice ­President-elect Mike Pence and others that he had not discussed the Obama administration sanctions on Russia for its interference in the 2016 election, the officials said. It is unclear what the White House counsel, Donald McGahn, did with the information.

Both the Washington Post and the New York Times reported that Flynn talked to the Russian ambassador, Sergei Kisilyak, about forthcoming sanctions from the Obama administration in response to Russian electoral meddling. The allegations led to calls from Democrats for Flynn to be dismissed while some prominent Republicans were tepid in their support.

When asked by reporters aboard Air Force One about the report, Trump replied: “I don’t know about that. I haven’t seen it. What report is that? I haven’t seen that. I’ll look into that.”

Flynn and the US vice-president, Mike Pence, had previously issued flat denials that Flynn and Kisilyak had spoken about anything of substance and the White House had insisted that the conversations involved only the exchange of Christmas greetings and preparations for a future Trump phone call with Vladimir Putin.

On Friday, Flynn’s staff at the national security council said he could no longer be sure whether sanctions had been discussed.

Democrat Adam Schiff, ranking member of the House permanent select committee on intelligence, said the resignation was inevitable and Flynn had been a “poor choice” for the role:

General Flynn’s decision to step down as national security adviser was all but ordained the day he misled the country about his secret talks with the Russian ambassador.

In fact, Flynn was always a poor choice for national security adviser, a role in which you need to be a consensus builder, and possess sobriety and steady judgment. It is certainly no role for someone who plays fast and loose with the truth.

But Flynn’s departure does not end questions over his contacts with the Russians, which have been alleged to have begun well before December 29. These alleged contacts and any others the Trump campaign may have had with the Kremlin are the subject of the House intelligence committee’s ongoing investigation.

Moreover, the Trump administration has yet to be forthcoming about who was aware of Flynn’s conversations with the ambassador and whether he was acting on the instructions of the president or any other officials, or with their knowledge.

Amid the uncertainty over Flynn’s future, several of the president’s top advisers, including chief of staff Reince Priebus and counsel Don McGahn, ducked in and out of late-night meetings in the West Wing.